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Omiya Mine

Niihori, Hidaka city, Saitama pref., Japan


Hidaka Mine


Pumpellyite-Actinolite facies bedded manganese deposit

Chert-hosted bedded manganese deposit in a chert block of the Early Cretaceous (130 Ma) Kashiwagi unit, a member of the Northern Chichibu accretionary complex. The kashiwagi unit has been subjected to Pumpellyite-Actinolite facies metamorphism as a low grade part of the Sambagawa metamorphic belt in the Late Cretaceous (100 Ma). The age of chert is Permian Guadalupian (270 Ma) or Late Jurassic (145 Ma). Ages of sedimentary rocks were determined by radiolarians, and metamorphic age by K-Ar or Ar-Ar radiometric dating of muscovite.

Omiya Mine

An adit is on the outcrop of bedded chert of the Kashiwagi Unit. The creek in front of this adit is buried by a huge amount of dump.

Reported Minerals

  • Pyrite
  • Calcite
  • Rhodochrosite
  • Rhodonite
  • Caryopilite
  • Unidentified mineral(white to pink, acicular)

Mineral Assemblages

  • Caryopilite - Rhodochrosite - Quartz
  • Rhodonite - Rhodochrosite - Quartz
  • Quartz - Hematite - Pyrite
  • Quartz - Rhodochrosite - Unidentified mineral


  • around 1900: Mn was mined in adits.
  • after 1945: Mined at an open pit.
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